Transcript SedPet 2014 composite c

Sediments form layers, called strata
Sedimentary Rocks
Ions weather out of rock,
are transported by
groundwater to sediment
layers below
Sediment grains moved to ocean by streams
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Ions transported
to lake or
Water enters pore
ocean
spaces between
sediment grains
Ion-rich
groundwater
LITHIFICATION
Compaction and
Cementation
Dissolved ions precipitate
to form cement between
sediment grains
Sedimentary environment determines roundness sorting, mineral diversity
Character of detrital sediments depends on time,
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distance, and energy. For example, in streams:
Particles are large and
irregular, and consist of
a variety of lithologies,
including the least
resistant.
Particles are mid-sized
and of intermediate
sphericity, and include
resistant and nonresistant
lithologies.
HIGHLANDS
LOWLANDS
Particles are small and
nearly spherical, and
consist mainly of the
most resistant lithologies,
such as quartz.
NEAR-COASTAL
Examination of minerals present and their sorting,
angularity, size and cements reveal the distance
from the source and local chemistry
Remember: sand 0.063 – 2mm
Gravels coarser
Muds less
Remember: sand 0.063 – 2mm
Gravels coarser
Muds less
http://logbase2.blogspot.com/2008
/08/log-calculator.html
500 mm = .5 mm
-1 x -1 is 1
log base 2 of .5 is -1
Wadell
roundness
Dott: % mud matrix
Dott: % mud matrix
Dott: % mud matrix
Micrite is a term used to describe lime mud, carbonate of mud grade. The term is also used in the
Folk classification to describe a carbonate rock dominated by fine-grained calcite.
Folk: bound by mud
or precipitated
calcite
Sparry cement: clear, relatively coarse-grained calcite in the interstices of any sedimentary rock
restrain or
regulate
When bound:
When bound:
Maturity
Ions and molecules in aqueous
solution are the raw materials fro
cements
• Blatt and Tracy page 232
• Recall that weathering makes
smaller grains, and chemical
weathering, especially
hydrolysis, dissolves feldspars
and micas leaving clays, metal
ions, and dissolved silica.
• Quartz is not effected except for
fragmentation and rounding.
• Thus a granite or granodiorite,
or compositionally equivalent
metamorphic rock, leaves
behind quartz and clay.
Transport
• The clays are FLAT microcrystals and spend
much of their time in suspension. Most end in
deep marine sediments over the long run.
DEMO sheet of paper
• Quartz fragments generally travel in the bed
load, so they are deposited, and frequently
buried, in a variety of non-marine and marine
environments, preserving less
common environments
Without rift valleys, we wouldn’t know much
about our own past.
http://people.uncw.edu/dockal/gly312/Fall2009/Labs/02Observation%20and%20Description%20of%20Graons.htm
Angularity
Using these ratios then you can apply
a name according to Folk (1974):
Under 0.60 very elongate
0.60 to 0.63 elongate
0.63 to 0.66 sub-elonate
0.66 to 0.69 intermediate shape
0.69 to 0.72 sub-equant
0.72 to 0.75 equant
Over 0.75 very equant
Grains become more rounded with time in transport
Fine sediments need still water to settle
What fills the spaces between grains?
Graywacke with matrix
Sandstone with hematite cement
Compaction (some dewatering)
and cementation
Diagenesis:
poikilotopic a crystalline sedimentary rock having multisized crystals, the larger
of which enclose small ones, often of a different mineral
Micritic – very fine grained; Acicular – needle like; Drusy - aggregate of minute crystals coating a
surface
Cements often control appearance
Sometimes Quartz from volcanic rocks (e.g. from Rhyolites) does NOT have undulatory
extinction because it was not strained
http://people.uncw.edu/dockal/gly312/sandstonepet/sandstone.htm
One crystal in the grain
Two or more crystals in the grain
http://en.wikipedia.org/wiki/Undulose_extinction
Chert grain - The subangular grain on the left is a chert fragment. Internally it is made
up of a mosaic of very small crystals ('cryptocrystalline') of quartz. As you rotate this
grain under polarized lights, there is a shimmering or flickering effect as each subgrain
of quartz goes in and out of extinction
Chert: many tiny “cryptocrystals” in the grain
Low cement SS are often very friable
Blue filter light shining through gaps with no cement
Here the cement completely fills gaps between grains
Chalcedony: microcrystalline Quartz
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_14.htm
Quartz Overgrowths- In this quartzite the individual quartz grains are
cemented together with a quartz (silicate) cement. Note that cement that
precipitated onto a quartz grain grew in 'optical continuity' with its substrate.
For example, the right quartz grain with the 'q' label seems to be a big white
blob. However, there is a faint dark line that outlines where the original,
rounded, grain boundary is. The outer most part of this grain is composed of
quartz overgrowth that is also white in this photo. If you rotated this slide under
polarized light you'd see that the entire grain, the ghost and its overgrowth, go
extinct together.
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_16.htm
Two phases of cementation - This is a quartz sandstone, seen under
plain light. The quartz grains have quartz overgrowths (labeled 'o'),
reflecting a first phase of cementation, and then, later, a period of
carbonate cementation (c) seen as a brownish material filling the pore
space.
http://www.gly.uga.edu/speleoatlas/SAimage0223.html
Calcite cemented sandstone (specifically, a
quartz arenite). Well-rounded quartz grains (Q)
have euhedral quartz overgrowths beyond
their original grain edges (arrows). Calcite (C)
has filled remaining pore space.
Note very high
interference color
of the Calcite.
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_17.htm
Calcite corrosion of Quartz - The light yellowish blue colored material here
is calcite cement. The black and speckled black blobs are quartz grains. The
edges of the quartz grains are corroded and filled in with the calcite cement.
Note that calcite tends to precipitate under high pH conditions, but that quartz
tends to dissolved under these conditions. So with high pH conditions this
type of erosion of the quartz grains with cementation of calcite can occur.
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_9.htm
Volcanic lithic grain (Lv) - This grain, seen under plain light, is nicely rounded and
internally you can see many, euhedral (i.e. with sharp angular crystal faces)
microphenocrysts of plagioclase (note the twinning on these euhedral grains). This
is a classic Lv grain, probably from a volcanic arc.
Folk Classification
R = rock fragments
http://faculty.gg.uwyo.edu/heller/Sed%20Strat%20Class/SedStratL1/slideshow_1_7.htm
Embayed plagioclase and calcite cement - The plagioclase feldspars here (note twinning) do
not have the nice perfectly round, smooth shape that they probably had originally. Instead the
grains have been 'embayed' (partially dissolved away) and calcite cement (bright bluish mosaic)
has filled in the embayment. This happens under high pH conditions, where calcite is precipitated
and silicates are dissolved. Imagine there were high pH conditions (leading to dissolving the
feldspar grains) but no carbonate rich ground water around (so no cement). You can see how
this would develop porosity in the sandstone while it was buried underground. Such 'secondary
porosity' can be abundant and makes those seeking hydrocarbons quite excited.
Litharenites are sandstones with a significant (>5%) component of lithic
fragments, symbol R or RF.Lithic sandstones are usually associated with one
specific type of lithic fragment (i.e., igneous, sedimentary, or metamorphic).
Lithic sandstones form in a wide variety sedimentary depositional associated
with active margins. This tectonic setting provides the source of the lithic
fragments, either through arc volcanism, thin-skinned faulting, or continental
collisions.
This can also occur when minerals are part of a sedimentary rock.
Resolves Fe++ content
Magnesium Calcite
Coarse carbonate grains called Allochems